Process for heat treating spheroidized steel



@July 18, 1939. 'w. J. CQNLEY 2,166,839

PROCESS FOR HEAT TREATING SPHEROIDIZED STEEL Filed Feb. 23, 1938 2 Sheets-Sheet l INVENTOR ATTORNEY July 18, 1939' w. J. coNLEY 2,166,839

PROCESS FOR HEAT TREATING SPHEROIDIZED STEEL Filed Feb. 23, 1938 2 Sheets-Sheetl 2 fo 600K.

INVENTOR www@ ATTORNEY Patented July 18, 19349' UNITED STATES PATENT OFFICE William J. Conley, Rochester, N. Y., assignor to E. Phelps Langworthy, Rochester, N. Y.

Application February 23, 193s, serial No. 191,915

2 Claims.

This invention relates to a process for treating spheroidized carbon and alloy steels to reiine, i. e., reduce in size, the large carbide spheroids thereby to render the said steels more suitable 5 for the purpose for which they are intended.

spheroidized steels are employed for a wide .variety of uses. Their desirable characteristics are, however, impaired or oiset in certain instances by the presence of the large carbide particles. It has been recognized, for example, that such particles have been primarily responsible for the principal difliculties (dulling of cutter, roughness of cut etc.) encountered in the machining of hard steels and that such difficulties would be overcome by effecting a reduction in the size of these particles. A reduction in the size of the large carbide particles not only renders thesteel more suitable for known uses but also renders it available for uses for which it would otherwise be wholly unsuited.

Heretofore, it has been assumed, and this has been based upon actual tests, that the heating of spheroidized steel caused the carbide particles to grow. I have discovered that while this, as a generality, is true these particles may be reduced in size by a heat treatment if thefactors of time and temperature are maintained within predetermined limits.

The principal object ofthe vpresent invention,

therefore, is a process for'heat treating spheroidized steel, carbon or alloy, in such a manner as to eifect a substantial reduction in the size of the carbide particles. f

The various views in the drawings are all accurate'full-size copies of photomicrographs of specimens (from the same piece of steel) which have been heat treated for different periods of time, the carbide particles being magnified 500 diameters in each instance.

4o Figure 1 illustrates the size of the carbide particles in the original piece of steel;

Figure 2 shows the size to which the said particles are reduced by the practice of the process;

Figure 3 illustrates the growth of the carbide particles when the steel is raised to the correct temperature but is not subjected to such temperature for a long enough period of time;

Figure 4 shows -the growth of the carbide particles when the steel is raised to the correct temperature but is maintained at such temperature for too great a period of time; and

Figure 5 shows the growth of the carbide particles when the specimen illustrated in Figure 2 was reheated after being heat treated in accordance with the process.

(Cl. 14S-21.5)

In the practice of the process any desired type of spheroidized carbon or alloy steel may be treated, the components and their percentages in each particular instance depending, of course, upon the use for which the steel is intended. The 5 steel, illustrated by Way of example in the photomicrographs, is die steel containing .90% carbon, 1.55% manganese and .30% molybdenum. The steel is heated in any suitable manner to a temperature, preferably of the order of 1250 F., and 10 between lower and upper limits of 1100 F., and 1400 F., respectively, and is maintained at such temperature for approximately three hours, the lower limit being the temperature at which no appreciable change in structure for the time spec- 10 ied occurs and the upper limit being the temperature at which -iron and manganese carbide go into solution.

The carbide particles are indicated in the drawings at 6. Figure 1 shows the size of the 2'! said particles originally while Figure 2 shows their size upon completion of the heat treatment of the process. That the large carbide particles have been broken up into substantially smaller particles is clearly shown by a comparison of 25 these figures.

The factor of time is critical as well as that of temperature. This is clearly illustrated by Figures 3, 4 and 5. The first shows the size of the carbide particles when the steel is heated to 1250 F. and immediately permitted to cool; Figure 4 shows the size of the carbide particles when the steel is heated to 1250 F. and held at this temperature for six hours, or three hours longer than prescribed by the process; and Figure 5 35 shows the size of the carbide particles when steel treated as called for by the process is reheated to 1250 F.' and held at this temperature for three hours. By comparing Figures 3, 4 and 5 with Figure 1 it will be noted that in each instance 40 the carbide particles are larger and more irregular than originally. The assumption that a heat treatment of spheroidized steels causes the carbide particles to grow is thus to a certain exten*I substantiated. 45

A comparison of the figures of the drawings shows that when spheroidized steel is heated to a temperature of the order of 1250 F. the carbide particles, at the outset, begin to grow and become more irregular in shape. As'the treatment 50 continues, however, the particles become more or less unstable and go through a stage of disintegration, increasing in numbers as they decrease in size. As the end of the three hour period approaches the breaking up process-slows up to a 55 point where it is negligible. The carbide particles remain in this reduced state unless the heat treatment is continued, in which case they begin to grow again. In other Words even though the steel be heated to a temperature of the specified value a reduction in the size of the carbide particles cannot be eiected unless the time factor is complied with. the said particles growing in size and becoming more irregular in shape if the time of the heat treatment is less than, or is extended beyond, that called for. The practice of the process, therefore, involves a termination of the heat treatment at a time when the carbide particles approach a condition when further disintegration cannot be eiected and before 'their growth begins anew.

I claim asmy invention:

1. The process of treating spheroidized steel Whichconsists in heating the steel to a temperature between 1100o E. and 1400c F. and holding the steel at such temperature for approximately three hours, thereby to cause the .large carbide particles to disintegrate into particles substantially smaller than the original large carbide particles.

2. The process of treating spheroidized steel which consists in heating the steel to a temperature of the order of 1250 F. and holding tbe steel at such temperature for approximately three hours, thereby to cause the large carbide particles to disintegrate into particles substantially smaller than the original large carbide particles.

WILLIAMf J. coNLEY. 

